Field of the invention
To produce shaped articles from organic hydrophilic polymer of high molecular weight such as gelatin or other natural or synthetic water-swellable hydrocolloids by a mechanical forming process such as die molding or injection molding it is often necessary to use process materials at high temperatures in order to obtain the plasticity needed for the mechanical forming process. Plasticity of water-swellable hydrocolloids is not only dependent on the temperature and on the rate of deformation but also on the water content. This latter is generally represented and strictly determined by the absorption isotherm of the process material, which, for each temperature gives the relative humidity of the surrounding gaseous medium which is in equilibrium with a given water content of the process material. Absorption isotherms are characteristic for any given process materials and depend on the chemical structure, molecular weight and degree of crosslinking between the molecules.
The relative humidity of the gaseous environment which is in equilibrium with a given water content of a swellable hydrocolloid is generally high at high temperatures.
Nevertheless, even at higher temperatures, the time needed to arrive at a given equilibrium may be very long, depending on the granularity and specific surface of the process material. For coarse-grained process materials many hours or even days may be needed to reach the equilibrium water content.
Such conditions, i.e. high relative humidity at high temperature may be detrimental for most known hydrocolloids, causing degradation e.g. by hydrolysis and other destructive processes. It is therefore highly desirable to reach the conditions of high temperature at any given water content of the process material in a time as short as possible.